I get a black box where the upload button is. Clicking the black box does open the file selector but it doesnt look good. your demo using flash shows the same.

 

http://ajaxuploader.com/demo/simple-upload-UI.aspx?UploadType=Flash

 

The only way I can get the blackbox to go away is to set UploadAddonButtonMode="Replace", but then the button no longer shows the hand cursor when hovering.

 

<CuteWebUI:UploadAttachments runat="server" ID="Attachments1" UploadType="Flash" MultipleFilesUpload="true" InsertText="" UploadCursor="Hand" UploadAddonButtonImage="../images/browse.gif" UploadAddonButtonMode="Replace" InsertButtonID="btnUpload" CancelButtonID="btnUploadCancel" OnFileUploaded="Uploader1_FileUploaded" OnUploadCompleted="Uploader1_UploadCompleted" NumFilesShowCancelAll="100"></CuteWebUI:UploadAttachments>